#include<iostream>
#include<vector>
#include<queue>
#include<cstring>
#include<cmath>
#include<map>
#include<set>
#include<cstdio>
#include<algorithm>
#define debug(a) cout<<#a<<"="<<a<<endl;
using namespace std;
const int maxn=4e5+1000;
typedef long long LL;
const LL mod=3;
inline LL read(){LL x=0,f=1;char ch=getchar();	while (!isdigit(ch)){if (ch=='-') f=-1;ch=getchar();}while (isdigit(ch)){x=x*10+ch-48;ch=getchar();}
return x*f;}
map<char,LL>map1;
LL fac[maxn];
LL ksm(LL a,LL k){
   LL res=1;
   while(k>0){
      if(k&1) res=res*a%mod;
      k>>=1;
      a=a*a%mod;
   }return res%mod;
}
LL C(LL n,LL m){
   if(m>n) return 0;
   return (fac[n]*ksm(fac[m],mod-2)%mod*ksm(fac[n-m],mod-2)%mod)%mod;
}
LL lucas(LL n,LL m){
    if(!m) return 1;
    return C(n%mod,m%mod)*lucas(n/mod,m/mod)%mod;
}
int main(void){
   cin.tie(0);std::ios::sync_with_stdio(false);
   fac[0]=1;
   for(LL i=1;i<=3;i++) fac[i]=fac[i-1]*i%mod;
   map1['B']=0;map1['W']=1;map1['R']=2;
   LL n;cin>>n;
   LL ans=0;
   for(LL i=0;i<n;i++){
      char op;cin>>op;
      LL d=map1[op];
      ans=(ans+d*lucas(n-1,i))%mod;
   }
   if(n%2==0) ans=(3-ans)%3;///ans*=(-1)^(n-1)
   if(ans==0){
      cout<<"B"<<"\n";
   }
   else if(ans==1){
      cout<<"W"<<"\n";
   }
   else if(ans==2){
      cout<<"R"<<"\n";
   }
   return 0;
}
